This invention pertains to power electronics design and manufacture. Specifically, the invention pertains to high current electrical connector designs that provide connections to Insulated Metal Substrate (IMS) circuit boards.
IMS circuit board materials are comprised of a metal substrate, usually aluminum or copper with a typical thickness from 0.040xe2x80x3 to 0.125xe2x80x3. A thin insulating material is bonded to the substrate and a layer of copper foil is bonded to the insulating material.
The IMS material is processed into printed circuit boards (PCBs) in much the same way as a typical fiberglass PCB where a photo mask is applied to the copper foil and the unwanted copper is chemically etched away, leaving the desired traces and pads.
For high power applications, IMS printed circuit boards have only one usable layer and are only suitable for surface mount components. Fiberglass boards can have many layers and a mix of through-hole and surface mount components. The value of the IMS material is in the very low thermal resistance from copper component mounting pad to the metal substrate. In high power applications, the substrate is in turn mounted to a heatsink. This allows surface mount semiconductor components such as transistors, rectifiers and SCRs to operate with low thermal resistance from device junction to ambient air. Low thermal resistance enables higher power to be processed with less silicon die area, which translates to lower costs.
There are two problems with the IMS materials for high power applications. First, the mechanical strength of the bond between the copper and insulating material and insulating material and substrate is limited. This weakness precludes the use of large, soldered, surface mounted terminals where high sheer and pull strength is required to reliably hold large cables. The prior art is to use multiple low-current surface mount connectors, pins or headers to make the transition to a fiberglass PCB. A single, high current, high mechanical strength termination could then be made on the fiberglass PCB. Second, the metal substrate layer is typically used only for mechanical support and heat transfer. It is desirable in most high power, high frequency switching applications to have a low impedance DC bus. This requires a two layer circuit board or other laminated bus assembly. The IMS material is limited by having only one easily accessible layer. In lower power applications an IMS board can be configured with a second copper layer but the heat transfer characteristics are compromised and the added cost may be prohibitive. Additionally, the problem of connecting large through-hole electrolytic capacitors to the to the circuit layers to achieve a low AC impedance bus is not solved.
The invention solves the two problems stated in the background discussion. First, a device will be disclosed that allows a high current connection to be made from an IMS printed circuit board to a wire or to a second printed circuit board. The connection will have high sheer and pull strength and is independent of the IMS insulating material bond strength. Second, a device and method will be disclosed for making a high current, low impedance, electrical connection from both the top copper foil and the IMS substrate to a second printed circuit board. This allows the IMS substrate to be used as an active circuit plane in conjunction with all or part of the top IMS copper foil to create a low AC impedance bus structure. This also allows a low AC impedance, coaxial connection with a fiberglass board where the fiberglass board is able to carry the larger through-hole components, such as electrolytic capacitors, relays and terminal blocks that the IMS board cannot.